The present invention relates to an improved foldable ladder structure and a method of manufacturing such foldable ladder structure and more particularly to a structure wherein at least one or more of several sections of a foldable ladder are formed from a shaped, integral and unitary structural material and to a method of forming such sections.
It is well known in the ladder art to make principal ladder sections of a complete ladder, such as the front step section and the rear back section, the support shelf and the spreader linkage from wood, aluminum, fiberglass or even plastic materials. It also is well known to assemble these several sections into a completed ladder wherein the sections can be moved relative to one another between a foldable or collapsed position wherein the front and rear sections are in adjacent face-to-face relation for transport and storage to an erected position wherein the lower portions of the front and rear sections are spaced apart with a spreader mechanism interposed between and connected to the front and rear sections serving to limit the spread or angle of opening and with a shelf connected to the upper part of one of the spread apart sections extended to support material thereon. The manufacture and assembly of the various and multiple parts of past ladders has been comparatively complex and difficult, requiring the separate cutting, sawing and finishing of numerous parts such as steps, braces, side rails, shelves, spreader arms, linkage mechanisms, hinges, wear treads, and trusses and gussets required to strengthen the several parts wherever needed. Further, the assembly of these numerous parts including but not limited to the steps of cutting, drilling, sanding, aligning, holding, bolting, nailing, gluing and otherwise fastening one part to another has been time and labor consuming, resulting in labor intensive products which have been comparatively expensive in manufacture and assembly, heavy for transport and bulky for storage.
One of several patents which illustrate past types of ladder structures is U.S. Pat. No. 821,391, issued to S. E. Wiltse on May 22, 1906, which broadly discloses hinged collapsible, erectable step members. In addition, a number of prior patents broadly suggest making one or more parts from plastic materials, such as can be seen in U.S. Pat. No. 3,042,140, issued to G. E. Basile et al on July 3, 1962; U.S. Pat. No. 3,744,591, issued to R. Lucci et al on July 10, 1973; U.S. Pat. No. 4,023,647, issued to R. C. Confer on May 17, 1977; U.S. Pat. No. 4,029,172, issued to A. Green on June 14, 1977; U.S. Pat. No. 4,124,093, issued to J. H. Breisch on Nov. 7, 1978; U.S. Pat. No. 4,193,476, issued to J. D. Emmons on Mar. 18, 1980; U.S. Pat. No. 4,215,766, issued to R. D. Littlefield et al on Aug. 5, 1980; and U.S. Pat. No. 4,244,760, issued to E. C. Smith on Jan. 13, 1981. As aforediscussed, the ladder structures as taught by these patents as well as other prior structures have been accompanied with undesirably complex and expensive manufacturing and assembly problems due to the number of parts involved and the number of assembly steps required.
The present invention (the novel designs for which are disclosed in copending design patent applications: Ser. No. D.710,479, filed Mar. 11, 1985; Ser. No. D.851,683, filed Apr. 14, 1986; and, Ser. No. D.852,500, filed Apr. 14, 1986) provides a unique ladder structure and a method of making the same which requires a minimum of sections to reduce manufacturing and assembly steps, which can be comparatively light in weight and compact for transport and storage but which is sturdy and of sufficient strength and stability to meet various industry standards and which is, at the same time, both electrically insulative and resistant to moisture and other weathering elements. The unique and novel apparatus and method of the present invention not only limits the number of parts required for efficient and economical manufacture but includes assembly features which allow for ready alignment and interchangeability and user features which allow for ready and sturdy erection, collapse, transport and storage, offering the required strength and stability with minimum wear and weather erosion.
Various other features of the present invention will become obvious to one skilled in the art upon reading the disclosure set forth herein.